Propellant and Explosives Production Method by Use of Resonant Acoustic Mix Process

ABSTRACT

A method to charge a container with an energetic mix is disclosed. This method includes the following steps: (a) adding a plurality of particulate energetic mix constituents and a binder to the container; and (b) mixing the plurality of energetic mix constituents utilizing a non-contact mixer to form a homogeneous mixture within the container, and curing the binder to solidify the homogeneous mixture and bind the homogeneous mixture to the container. The container may be a liner or pre-form intended for insertion into a device, or may form a portion of the device itself, such as an aft portion of a rocket motor or casing for an explosive device. Because the resonant mixer does not have a moving impeller or other component that contacts the energetic mix and the container is not reused, there is minimal decontamination required between each mix and the manufacturer may rapidly commence assembling the next device, rather than clean-up and recertification.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No. 60/983,621, filed Oct. 30, 2007, which is incorporated by reference as if disclosed herein in its entirety.

BACKGROUND

1. Field

This invention relates to a method to charge a container with energetic ingredients to produce solid propellants, explosives, or other energetic compositions. More particularly the energetic mixing is by non-contact means by achieving resonance of the ingredient slurry in batches, in near net shape containers, or in end-use containers such as rocket motor cases, warheads, or explosive liners.

2. Description of the Related Art

The preparation and loading of a propellant for a rocket motor or missile is a complex process requiring many steps and a significant amount of time. One conventional process includes the following steps: (a) preparing a submixture that includes a prepolymer, plasticizers and stabilizers; (b) forming a premixture by adding a fine aluminum powder to the submixture; (c) transferring the premixture to a mix bowl; (d) initiating batch mix by sequentially adding an oxidizer, such as ammonium perchlorate; (e) interim mixing under a vacuum to degas propellant slurry; (f) adding propellant curatives and catalyst; (g) final mixing and vacuum degassing propellant slurry; (h) transporting batch mix to casting area; (i) establishing cast tooling, conducting propellant transfer and casting propellant in motor case(s); (j) transporting cast motors to cure facility; (k) curing motors at elevated temperature, typically about 65° C.±15° C. for an extended period of time, typically from 4 to 21 days; (l) removing cured motors for post-processing and delivery to customer; and (m) decontaminating mix and cast equipment, and certifying for reuse.

The combined time for the three mixing steps, (d) batch mix, (e) interim mix, and (g) final mix, is on the order of 36±6 hours, especially for batches containing state of the art amine-type bonding agents. The period of time is dependent on various interim chemical reactions that proceed to achieve the final required or optimum cure properties in finished product. The extended period of time required for mixing and curing, as well as the time and expense for decontamination and recertification of tooling for reuse, make the conventional process time consuming and expensive.

A low frequency, high acceleration vibratory mixer is disclosed in U.S. Pat. No. 7,188,993 to Howe et al. The frequency can be adjusted to produce standing acoustic waves and resonant mixing greatly agitating fluids and/or solids leading to enhanced mixing at reduced times when compared to conventional mixing techniques. Further, the mixing does not require a rotating impeller to contact the mixture. U.S. Pat. No. 7,188,993 is incorporated herein by reference in its entirety.

An acoustic wave generating mixer of the type disclosed in U.S. Pat. No. 7,188,993 is disclosed in an MDA Update, summer 2004, and is used to blend metallized powders, gallants and liquids into a finished gel propellant, which is typically prepared by addition of gallants and metal powders to liquid fuels, or, alternatively, by addition of liquid oxidizers to particulate gallants, followed by final vacuum mix, and transfer to storage tanks. Although the mixing of metallized fuel gels or particulate-gelled oxidizers is facilitated, no cure chemistry is accommodated, nor is cured solid propellant or explosive fill castable compositions as a result.

BRIEF SUMMARY OF THE INVENTION

Accordingly, there is provided a method to charge a container with an energetic mix. This method includes the following steps: (a) adding a plurality of particulate energetic mix constituents and a binder to the container; and (b) mixing the plurality of energetic mix constituents utilizing a non-contact mixer to form a homogeneous mixture within the container, and curing the binder to solidify the homogeneous mixture and bind the homogeneous mixture to the container.

The container may be a liner or pre-form intended for insertion into a device, or may form a portion of the device itself, such as an aft portion of a rocket motor or casing for an explosive device. Because the resonant mixer does not have a moving impeller or other component that contacts the energetic mix and the container is not reused, there is minimal decontamination required between each mix and the manufacturer may rapidly commence assembling the next device, rather than clean-up and recertification.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects and advantages of the invention will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates in flow chart representation steps to prepare an energetic mix utilizing an acoustic mixer.

FIG. 2 illustrates a liner containing energetic mix ingredients in accordance with the layer step of FIG. 1.

FIG. 3 illustrates a liner containing dispersed energetic mix ingredients in accordance with the resonant acoustic mix step of FIG. 1.

FIG. 4 illustrates a liner containing an energetic mix in accordance with the cure step of FIG. 1.

FIG. 5 illustrates a rocket motor case as a mixing chamber for the process of FIG. 1.

FIG. 6 illustrates an explosive device housing as a mixing chamber for the process of FIG. 1.

FIG. 7 illustrates an alternative liner containing energetic mix ingredients in accordance with the layer step of FIG. 1.

Like reference numbers and designations in the various drawings indicated like elements.

DETAILED DESCRIPTION

FIG. 1 shows a process to produce an energetic mix utilizing an acoustic mixer in flow chart representation. FIGS. 2-4 illustrate a liner filled with components of the energetic mix at different stages of the process.

With reference to FIGS. 1 and 2, all components of the energetic mix are layered 10, or simultaneously added as preblends of liquid or solid ingredients, or variations of these, in a suitable container 12. The container 12 may be a liner or pre-form that is subsequently inserted into a deliverable container, or a device housing itself. As shown in FIG. 7, the container may also hold cores, mandrels 13 or other formers which allow tailoring of the mix vortices within the resonant mix container, or formers inserted to allow cured compositions to have various end-use configurations of specific thrust, duration, or explosive yield (by orientation of container interior features, upon cure, to direct combustion or blast). Further, the container itself may be tailored by stiffness factors to enhance the resonant mix by attaining a resonant response to assist the mix process. Referring back to FIGS. 1 and 2, the layered 10 configuration may constitute any number of layers. Exemplary is first layer 14, second layer 16, third layer 18 and fourth layer 20 as shown in FIG. 2. Note that container 12 in FIG. 2 has a portion of one wall removed to illustrate the contained layers. Each layer is a component of the energetic mix or binder and preferably, all components are added at layer step 10, such that further additions to container 12 are not required.

Each addition may be a dry particulate or a liquid, as one component or blends of two or more solid or liquid ingredients, varied to provide optimum mix of specific formulations for each purpose, either as propellant or explosive compositions. Components may be premixed or added non-sequentially to enhance manufacturability throughput, reduce hazards, or reduce cost by pre-processing by separate automated techniques in other optimized facilities.

In an exemplary energetic mix for use as a (castable) composite aluminized propellant; First 14, liquid or solid prepolymer, liquid plasticizer, liquid and/or solid stabilizers, aluminum powder, liquid bonding agents, possibly preblended as nonenergetic materials in appropriate low-cost facilities, approximately 30 weight percent; second 16, particulate or encapsulated oxidizer particles having a variety of size distributions to achieve specific ballistic performance, approximately 69 weight percent; and third 18, liquid curatives and liquid or solid cure catalysts or cure modifiers, approximately 1 weight percent.

With reference to FIGS. 1 and 3, the components of the energetic mix are next subjected to a resonant mix 22. As an option, external heat or cooling, or vacuum, or applied gas pressure may be applied to the resonant mix. As disclosed in the aforementioned U.S. Pat. No. 7,188,993, mixing is done in a resonant mix process resulting from a combination of vibration and acceleration of the container 12 and contained components of the energetic mix. Resonant mixing does not require the use of stirrers, paddles or mix blades and no part of the mixer contacts the energetic mix greatly simplifying clean up and preparation for a next run. Due to rapid mixing achieved by the formation of acoustic waves within the components of the energetic mix, thorough mixing is accomplished in minutes, rather than the hours required with state of the art conventional mixing processes. Resonance is an additive effect of small periodic vibrations resulting in vibrations of significantly larger amplitude and results in more homogeneous mixing of the components and a knitting cure behavior causing interlocking of the solid components. Resonant mixing process also makes stable multi-phase compositions such as emulsions, gels, plastisols, thermosets, or thermoplastic compositions with solid, liquid or gel-phase ingredients that may all be mixed at same time.

A vibratory mixer 24 contains a plurality of oscillator drives (not shown) that transfer vibration and acceleration to the container 12 by way of variable resilient members 26, such as springs at a frequency and amplitude effective to cause resonance. By way of example, the exemplary composition described above is effectively transformed to a substantially homogenous mix 28 by resonant mixing for a time of from 30 to 60 minutes at a frequency between 40 and 70 cycles per second and a linear motion between 20 and 60 grams per cycle.

Referring now to FIGS. 1 and 4, the substantially homogenous mix is next cured 30. Preferably this cure is at ambient temperature, nominally 20° C.-25° C. for a time sufficient to form a coherent mass 32 within, and bonded to, container 12. The container is then delivered 34 to a customer. As such, there are no mixing bowls that require decontamination prior to additional use. Rather, a next container may immediately be employed to repeat the process. Alternatively, the coherent mass 32 is stripped 35 from the container prior to shipment to a customer.

The container 12 may be a liner or preform that is then inserted into a desired product, such as a housing of a rocket motor, or other projectile for artillery use, or an explosive device for shape charge applications. Alternatively, as illustrated in FIG. 5, a segment or case section (with or without forward or an aft closures), such as portion 36, configured as end-burning or affixed to a mandrel allowing center-perforation as a cylindrical propellant grain may be used. The coherent propellant or explosive mass 32 can therefore be blended and simultaneously formed within the propulsive or explosive device, such as for shaped charge device 40, as illustrated in FIG. 6. Casing 42 of the explosive device forms the container for producing the energetic mix and a shaped liner 44 may be added before the cure step is completed to cause the coherent mass 32 to bond to the interior side of the liner 44. As a non-comprehensive list, other battlefield items requiring energetic preparation, such as artillery shells, mortars, grenades and reactive armor are enhanced by the process described herein.

One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, elastic cases or containers having predesigned flexibility or elasticity may be selectively used in whole or in sections to allow variations in the mix resonance, establishing flow patterns that can be tailored, especially when used together with rod-like or fibrous ingredients, to build burning rate control of the end product during the mix process via selective orientation of the mix ingredients due to resonant mix patterns. Accordingly, other embodiments are within the scope of the following claims. 

1. A method to charge a container with an energetic mix, comprising the steps of: adding a plurality of particulate energetic mix constituents and a binder to said container; mixing said plurality of energetic mix constituents utilizing a non-contact mixer to form a homogeneous mixture within said container; and curing said binder to solidify said homogeneous mixture and bind said homogeneous mixture to said container.
 2. The method of claim 1 wherein said energetic mixture is selected to be effective to propel a projectile.
 3. The method of claim 2 wherein said container is selected to be a rocket motor.
 4. The method of claim 3 wherein said container is selected to be a liner for a rocket motor.
 5. The method of claim 2 wherein acoustic waves achieving resonance conditions are utilized for said mixing.
 6. The method of claim 5 wherein said step of curing said binder is at ambient temperature.
 7. The method or claim 6 wherein said binder is selected to include at least one member from the group consisting of functional prepolymers, plasticizers, stabilizers, cure catalysts, thermoplastic compositions and ballistic modifiers.
 8. The method of claim 7 wherein said propellant is selected to include at least one member selected from the group consisting of metal fuel powders, solid oxidizers in dispersions or emulsions, liquid oxidizers in dispersions or emulsions and tailored ingredients having aspect ratios or shapes effective for ballistic control of curable mixes.
 9. The method of claim 1 wherein said energetic mixture is selected to be effective as an explosive.
 10. The method of claim 9 wherein said container is selected to be a resin plus fiber composite.
 11. The method of claim 9 wherein said container is selected to be a liner for a propulsive device that is integrated with an artillery shell, mortar, grenade, reactive armor, or other battlefield item requiring energetic preparations.
 12. The method of claim 9 wherein acoustic waves achieving resonance conditions are tailored for use in said mixing step.
 13. The method of claim 12 wherein said step of curing said binder is at ambient temperature.
 14. The method or claim 13 wherein said binder ingredients respond to knitting cure behavior as a result of organic, inorganic, or organo-metallic additives facilitating polymer cure acceleration mechanisms.
 15. A method to produce an energetic mix, comprising the steps of: adding a plurality of particulate energetic mix constituents and a binder to a container; mixing said plurality of energetic mix constituents utilizing a non-contact mixer to form a homogeneous mixture within said container; and removing said homogeneous mixture from said container.
 16. The method of claim 15 including the step of curing said binder to solidify said homogeneous mixture prior to said removing step.
 17. The method of claim 15 wherein acoustic waves achieving resonance conditions are utilized for said mixing.
 18. The method of claim 16 wherein said step of curing said binder is at ambient temperature.
 19. The method or claim 14 wherein said binder is selected to include at least one member from the group consisting of functional prepolymers, plasticizers, stabilizers, cure catalysts, thermoplastic compositions and ballistic modifiers.
 20. The method of claim 19 wherein said propellant is selected to include at least one member selected from the group consisting of metal fuel powders, solid oxidizers in dispersions or emulsions, liquid oxidizers in dispersions or emulsions and tailored ingredients having aspect ratios or shapes effective for ballistic control of curable mixes. 